The present invention relates to a display device, and in particular, relates to a liquid crystal display device which ensures three dimensional display using a liquid crystal lens.
Generally, a liquid crystal display panel includes a TFT substrate having pixel electrodes and thin film transistors (TFT) arranged in a matrix, and a counter substrate that faces the TFT substrate and has color filters at the positions corresponding to the pixel electrodes of the TFT substrate, and interposes a liquid crystal between the TFT substrate and the counter substrate to form a display region. An image is formed by controlling a transmittance of light through liquid crystal molecules for each pixel. As the liquid crystal is capable of controlling only polarization light, the light from the backlight is polarized by a lower polarizing plate before incidence on the TFT substrate, and is controlled by the liquid crystal layer. It is then polarized by an upper polarizing plate again so as to be externally emitted. As a result, the light is emitted from the liquid crystal display panel as the polarization light.
Various kinds of methods of three dimensionally displaying an image to be formed on the liquid crystal display panel have been proposed. Among all, the method of forming a liquid crystal lens on the liquid crystal display panel especially applied to the compact display device has received attention because of reasons that no special eyeglasses are required for visually identifying the three dimensional image, the method allows switching operations between the two dimensional image and the three dimensional image, and the like.
Japanese Patent No. 2862462 discloses that the liquid crystal lens is configured by interposing liquid crystal molecules between the upper and the lower substrates, forming a strip-like upper substrate electrode pattern on the upper substrate, and a solid planar lower substrate electrode pattern on the lower substrate, and orienting the liquid crystal molecules along the electric field generated by applying a voltage to the upper and the lower electrode patterns.
JP-A-2009-520231 discloses the liquid crystal lens formed by using the electric field generated as the vertical electric field between the upper and the lower substrate electrode patterns. In this case, the upper and the lower substrate electrode patterns are substantially the same except that the pattern on the upper substrate is rotated to be at a right angle to the pattern on the lower substrate. This makes it possible to adjust direction of the lens at 90° using the method of applying the voltage to the upper and the lower substrate electrode patterns so as to allow the three dimensional display on both horizontal and vertical views.
FIGS. 15 to 17 illustrate an outline of a liquid crystal lens 10 and a 3D display using a liquid crystal lens 10. The term “2D display” refers to the two dimensional display, and the term “3D display” refers to the three dimensional display herein. The liquid crystal lens 10 is configured to interpose the liquid crystal between two substrates each having electrodes, and has the same structure as that of the liquid crystal display element. However, unlike application to the liquid crystal display for display purpose, the subject lens is not configured to control the polarizing direction, and accordingly, no polarizing plate is used.
FIG. 15 represents an outline of the electrodes formed on two substrates that interpose the liquid crystal. A laterally long rectangular pattern indicated by a solid line denotes an electrode 31 on a lower substrate 30. A rectangular pattern indicated by a broken line denotes an electrode 21 on an upper substrate 20. Rectangles marked with A, B and the like denote electrode terminals which apply voltage from outside. Lines that connect the electrode terminals and the electrodes on the substrates denote wirings. The electrode connected to the electrode terminal A may be referred to as an electrode A, and the one connected to the electrode terminal B may be referred to as an electrode B herein. In this case, the patterns on the upper and the lower substrates may be inverted because of no essential limitation. However, as it is necessary to transmit light rays, at least the electrode that covers an entire display part is formed using a transparent electrode such as an ITO.
An arrow 40, 41 shown in FIG. 15 indicates rubbing directions of the upper and the lower substrates, which are the same. The liquid crystal to be interposed between those substrates is oriented so that the longitudinal axis is directed to the arrow direction in the state where the voltage is not applied. FIG. 16 is a sectional view taken along line Y-Y of FIG. 15. The electrodes on the lower substrate 30 are set so that two pixels of the liquid crystal display panel below the liquid crystal lens 10 are disposed between two electrodes. Actually, the pitch of the two pixels is not the same as that of the electrodes. Those pitches are appropriately designed in accordance with a possible view point.
FIG. 16 illustrates the state where the upper and the lower electrodes are at the same voltage level, that is, no voltage is applied to the liquid crystal or the liquid crystal lens 10 is in OFF state. In this state, the liquid crystal is overall directed to the orientation direction regulated by rubbing. Then the liquid crystal lens 10 serves as an optically uniform medium with respect to the transmitting light, and no action occurs. That is, the 2D image on the liquid crystal display panel for display purpose is output as it is.
FIG. 17 illustrates the state where the voltage is applied to the upper and lower electrodes of the liquid crystal lens 10, and the orientation direction of the liquid crystal is changed, that is, the liquid crystal lens 10 is in ON state. In this state, likewise the normally operated liquid crystal display panel, the AC voltage is applied in order to prevent deterioration of the liquid crystal. The solid electrode is formed on the upper substrate 20, and the localized electrodes are formed on the lower electrode. Therefore, the electric field applied to the liquid crystal is not uniform in the vertical and horizontal directions shown in the drawing. Then the liquid crystal molecules are radially oriented as illustrated in the drawing along the radial (parabolic) electric field from the lower localized electrodes to the upper solid electrode.
The liquid crystal molecules 50 exhibit a birefringent property. The content of the polarization of passing light in the longitudinal direction (longitudinal axis) is brought into an extraordinary ray with high refractive index. The content in a direction perpendicular to the aforementioned content is brought into an ordinary ray with lower refractive index than the extraordinary ray. The angle defined by the contents may be considered through decomposition into the extraordinary ray content and the ordinary ray content in the same manner as vector decomposition. The lens as illustrated in FIG. 17 may be derived from the birefringent property.
If a polarizing direction 42 of the incident light, that is, the light emitted from a liquid crystal display panel 100 is substantially in parallel with the rubbing direction of the liquid crystal lens 10, the rate between the high refractive index part (extraordinary ray part) and the low refractive index part of the incident light upon its passage through the liquid crystal lens 10 may vary depending on the location.
The broken line indicating an interface of a convex lens 11 illustrated in FIG. 17 schematically shows the interface between the high refractive index part and the low refractive index part. The resultant lens provides the same effect as that of the convex lens in the liquid crystal. Under the effect of the convex lens, when two pixels of the liquid crystal display panel 100 are provided as shown in FIG. 17, the light ray from a first pixel 200 mainly changes its path toward the upper right side, and the light ray from a second pixel 300 mainly changes its path toward the upper left side. Referring to FIG. 17, each of codes r, g and b of the first pixel 200 and the second pixel 300 will herein denote a red sub-pixel, a green sub-pixel, and a blue sub-pixel, respectively. The light ray from the first pixel 200 may be guided to a right eye and the light ray from the second pixel 300 may be guided to a left eye of an observer by displaying signals of the first pixel 200 and the second pixel 300 for right and left eyes, respectively through appropriate design of the liquid crystal lens 10 and the liquid crystal display panel 100. The resultant image may be identified as the 3D image by the observer.